How to sum elements in a matrix rowwise for specific columns only?

2018 6 5
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更新时间：2020 4 7
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I have a matrix X, consisting out of 100 rows and 10 columns. I want to sum up columns 7 to 10 to one single number, yielding a matrix with still 100 rows, but only 7 columns.

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Stephen23
Stephen23 2018-6-5
编辑：Stephen23 2018-6-5

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Where X is your matrix:
Y = [X(:,1:6),sum(X(:,7:10),2)]

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stanley ho
stanley ho 2020-4-7
编辑：stanley ho 2020-4-7
can you explain what does the 2 stands for in (sum(X(:,7:10),2).
Thank you very much! :)
Stephen23
Stephen23 2020-4-7
编辑：Stephen23 2020-4-7
"S = sum(A,dim) returns the sum along dimension dim. For example, if A is a matrix, then sum(A,2) is a column vector containing the sum of each row."
https://www.mathworks.com/help/matlab/ref/sum.html#btv6ok6-1-dim

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